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In Windows NT there is a command-line utility
(ipconfig) that lets you see the
current ip configuration. Is there a utility in Linux for
this? —Skip Bigelow, sbigelow@aarp.org

Even though there are graphical tools to give the information
you've asked (including Red Hat's
netcfg command), you can always
use /sbin/ifconfig. It will give you detailed
information regarding all active interfaces (ethernet, ppp,
loopback etc.). —Mario, mneto@argo.com.br

Sharing a Cable Modem

I have been browsing many different Linux web sites to look
for any FAQ or guide on this topic: How to share a cable modem
connection at home between a Linux and a Windows machine, which is
where the cable modem installed. I would appreciate it if you would
give me some pointers. —Samuel Fung, samfz@hotmail.com

I would move the cable modem to the Linux machine and share
it with your other computers from there. Why? Because Windows has
no provision, off the shelf, to serve as a router, enable security
features such as packet filtering, masquerading, forwarding, etc.,
while Linux does all that quite naturally and quite well. You do
not specify the cable modem you have, but I would suggest looking
at
http://www.linuxdoc.org/
for documents on networking and connecting network devices to your
Linux box. After that, look at the how-to articles on connecting to
an ISP. —Felipe Barousse, fbarousse@piensa.com

Booting without Messages

Is it possible to turn off the kernel boot-up messages?
—Nicholas, vunch@pacific.net.sg

The easiest way is to set console=ttyS3,38400n8, or something
similar, on the LILO command line to redirect console output to a
serial port. —Marc Merlin, marc_bts@valinux.com

Root Compromise

When I tried to log in to my Linux box this morning, I was
surprised to find out that I was no longer able to do this. The
login prompt appears as usual, but when I type the user name and
press Enter, instead of the password prompt a new login prompt
appears. No messages appear except a line that says:
/var/hackr0x/login: No such file or directory.
This line disappears so quickly that I had to repeat the procedure
of typing the user name a couple of times in order to decipher
it. —Victor, victor@angolatelecom.com

Your machine was indeed compromised. At this point you don't
want to fix your machine, you just want to get your data off and
re-install it. You don't know what's been modified nor how. In
cases where you can't log in at all, you can always boot with
linux init=/bin/bash at the LILO prompt, and
then do: mount -wno remount/mount -a
/etc/rc.d/init.d/network start (if you want to back up
data over the Net). You can also boot from a rescue floppy or CD.
Once you get your machine re-installed, do not just connect it to
the Internet again without securing it properly. Make sure you have
all the updates installed; do not run any unnecesary dæmons,
and firewall the machine if possible. —Marc Merlin,
marc_bts@valinux.com

Every major distribution has an “announce” list for
security updates. After you reinstall, get on the list for the
distribution you run. Also, remove unused software—it's the
cheapest, fastest security precaution you can take. —Don Marti,
dmarti@linuxjournal.com

Slash Notation for Netmasks

Nowadays I'm working with Linux firewalls, and I'm
configuring one in a client organization. I found the following
lines in the script that applies the rules of the firewall
(IPCHAINS):

INT0="eth0"
IP0="192.168.1.125/24"
NET0="192.168.1.0"

What is “/24” in the IP number?

Also can I put two networks in the same variable? For
example:

NET0="192.168.1.0,192.168.10.0"

—Fabio Losnak, fabiolosnak@yahoo.com

The “/24” in the IP number means the network 192.168.1.0
with a netmask of /24 or 255.255.255.0. You probably cannot put two
networks in the same variable but that would really depend on the
script that is parsing this. —Marc Merlin,
marc_bts@valinux.com

Can't Unlink Files

As root, I cannot get rid of the following files; they should
belong to the deb package r-base, but in this case they seem to be
some kind of links:

I get a message like cannot unlink. operation not
permitted —Odoardo Zecca, odoardo.zecca@galactica.it

You had some file system corruption. chattr -i
*.tex should remove the incorrectly set immutable flag
and let you delete the files. —Marc Merlin,
marc_bts@valinux.com

Restricting E-Mail Accounts with
Sendmail

I have a mail server (RH 6.2, Sendmail Single Switch) acting
as a smart relay on our DMZ. Internally, we have a mail server (RH
7.0, Sendmail Single Switch) that acts as both an SMTP and POP3
server.

We need to be able to differentiate between local-only and
WAN e-mail accounts. Local-only accounts would be limited to local
delivery/receipt and WAN accounts would be granted access to the
world for inbound and outbound mail.

To further complicate matters, all users
should have the format of first.last@domain.com for e-mail
addresses. Is there a method of doing this within the capabilities
of Sendmail or, if not, what package(s) will allow me to do
this? —Michael Phillips, mike.phillips@ieionline.com

There are many approaches to solve your riddle. For instance,
an easy one would be to restrict e-mail relaying with the
/etc/mail/access file on an client IP address basis. Your actual
request is not a complex one, you just need a bit of a planning on
your network layout, the addressing scheme and a bit of tuning on
the Sendmail side. Go to the
http://www.sendmail.org/
site and look for all relaying-related documents. That will help
you solve your requirements. —Felipe Barousse,
fbarousse@piensa.com

Telnet Sessions Time Out

Is there a Telnet time-out setting on Linux? My sessions time
out after about five minutes. —Jan Dubroca,
jan.dubroca@delta-air.com

You are probably Telneting outside of your network, through
an IP masquerading server that times out TCP connections after five
minutes. On Linux, the fix for this (on the firewall) is:

I don't believe that there is a tim-eout setting for Telnet.
I assume that what's timing out is your shell. The shell time-out
can be set in /etc/profile. My guess is you've
got an entry that looks something like this:

TMOUT=300

The value here is in seconds. You can change this
to give yourself more time or simply remove the line to disable
shell time-out completely. —Paul Christensen,
pchristensen@penguincomputing.com

Loading vmlinuz, Then Nothing

I used Red Hat 6.0 to install Linux. I booted the machine
from CD-ROM successfully, and I pressed Enter after boot: This
message appeared:

Loading initrd.img.....................
Loading vmlinuz........

Then the computer stopped.

When I booted my computer from the floppy disk (Win98
bootdisk), I ran the /dosutils/autoboot from the
Red Hat CD-ROM. Unexpected, it appeared that I had installed Linux
successfully and even configured the X Windows System well. In the
end, the computer told me:

Congratulations, you have installed linux successfully,......
The system reboot....

And when it rebooted, this message appeared:

Loading linux..........

Then the computer stopped again.

I have also tried Red Hat 5.0, Bluepoint1.0 and 2.0,
TurboLinux, Slackware. The results were all the same. WHY?
—ekun, xx@public1.ptt.js.cn

Apparently, you can boot Linux from
loadlin (which you did when you
started the Linux install from Windows), but, for some unknown
reason, it fails when you boot with LILO. One option is to do an
install from Windows, like you already did, and then boot from the
RH rescue CD-ROM. Copy your kernel (in/boot) to
the Windows partition (which you will need to mount too). Copy and
configure loadlin (you should have them on your RH CD-ROM), and use
loadlin to boot Linux. A sample loadlin config from my system looks
like this:

I've seen this happen as the result of booting a kernel
that's optimized for the wrong processor, but if this is happening
right away after a fresh install (in fact, after EVERY install of
any of a number of distributions) you most likely have a serious
hardware problem. You should try different RAM if you have any
available. I can't say for sure that the RAM is the culprit, but
that's where I'd start. —Robert Connoy,
rconnoy@penguincomputing.com

Recompiling the Kernel

I have installed an IDE Atapi Zip drive and need to know how
to have Linux to find it. I have tried to recompile but get the
following error:

Makefile Makefile: 213 arch/i386/Makefile:
No such file or directory
Makefile: 481 Rule make: No such file or directory
make *** No rule to make target Rules.make. Stop

—Bob Parry, robpar@telus.net

Did you read README in /usr/src/linux? You
compile a kernel like this:

make menuconfig; make clean; make dep;
make install; make modules; make modules_install

More details can also be found here:
www.linux.com/howto/Kernel-HOWTO.html.
If you already have the right module compiled,
modprobe ide-floppy
should do the trick. —Marc Merlin, marc_bts@valinux.com

I Have No Dæmon, and I Must Print

When I try to send anything to the printer, I get
Job is queued, but cannot start dæmon. I
can print by sending text directly to the printer with
cat, but it won't start the
dæmon. lpc status shows no dæmons started. I've set up
printers many times before, but I've never run into this problem.
I've tried removing and reinstalling the lpr package and all of the
other tricks I've read. Even—Jim Jerzycke, kq6ea@amsat.org

Make sure that the printer spooler dæmon is running.
With SuSE you'll want to make sure that the file
/etc/rc.config includes the line

START_LPD="yes"

If it is not there, or if it is set to no, you
should make the change, and then run—Robert Connoy,
rconnoy@penguincomputing.com